Note
$14.95 was a lot of money in 1960, but the HD-20 sold well, with a run of 16 years. Inside this little box are a 100 kHz crystal, a single transistor oscillator, and a 9-volt battery, NEDA type 1600. A modern 9-volt battery (NEDA type 1604) could easily be substituted, given the proper connector.
The HD-20 puts out accurate markers from 100 kHz to more than 54 MHz and calibrates to WWV with a small trimmer on the back. Many of these have been unnecessarily user modified for external power.
The binding post cap originally was red and early units were fitted with metal TX-1-style knobs. Later models used a small gray plastic knob of the style shown on the AC-1. Be sure to check for battery damage (the back is open). Finished in two-tone green.
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
